Tube and fitting assembly and method of making same

ABSTRACT

A tube and fitting assembly is disclosed which includes a plastic fitting with a hollow pin frictionally receiving an end portion of a plastic tube, and an integral collar surrounding the pin and tube end portion and with the tube end portion clamped between the pin and collar. A method of making a tube and fitting assembly is disclosed which includes spin-forming the collar of a fitting about an end portion of a plastic tube while the end portion is disposed on a hollow pin concentric with the collar.

TECHNICAL FIELD

This invention relates to tube and fitting assemblies and, moreparticularly, to an improved tube and fitting assembly and to animproved method of making a tube and fitting assembly.

BACKGROUND ART

Medical tube assemblies such as employed in or used as catheters, fluidtransfer tubes and the like, generally use a tube fitting with a luerconnector at one end for connecting the tube or catheter to anotherfluid device in a fluid system.

The tube and fitting obviously should be so connected together that theydo not separate or result in fluid leakage under mechanical pullingforces and fluid pressures that may be encountered when the assembly isin use. However, such failures have been encountered, especially whenthe tube and fitting are of a relatively small size.

One method of connecting the tube and fitting together is to provide thefitting with a recess or bore and solvent bond the outer surface of oneend of the tube to the walls of the recess. With such an assembly,however, any separating forces or pulling force on the catheterencountered when in use tends to narrow the catheter, resulting ininward forces tending to pull the catheter inwardly away from the recesswalls. Such connections have not been entirely satisfactory, especiallywhere the tube is of small diameter. Also, the solvent generally weakensthe catheter and fitting at the connection. Furthermore, with such amethod the inner diameter of the recess and the outer diameter of thetube must be held to close tolerances, further complicating themanufacture of such an assembly.

Another method employed is to bond the inner surface of one end portionof a tube to the outer surface of a hollow pin. With this method, thesolvent tends to weaken the walls of both the pin and the tube,resulting in a weak connection between the fitting and tube, especiallywhere the tube and pin are of relatively small diameters and the wallthicknesses of the pin and tube are small.

The use of solvents and adhesives in obtaining a fluid-tight connectionbetween a tube and fitting also has the disadvantages of producing fumesand odors, and such materials are not easily employed and must bestored.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide animproved tube and fitting assembly, and method of making the same, whichovercome one or more of the above problems.

Another object of the invention is to provide an improved method ofconnecting a plastic tube and plastic fitting to obtain a strong,fluid-tight connection between the tube and fitting and without the needof solvents or adhesives.

In accordance with one aspect of the present invention, a method ofmaking a tube and fitting assembly is disclosed which includes the stepsof providing a plastic fitting having an end socket and a hollow pinextending concentrically within the socket, and inserting one endportion of a tube into the socket and onto the pin. A die is providedhaving a die-forming cavity narrowing toward one end. While effectingrelative rotation and axial movement of the tube and fitting, thefitting moves into the die-forming cavity and is urged in a directiontoward the narrow end so that the outer surface of the walls of thesocket engage the walls of the opening and are inwardly formed againstthe outer surface of the end portion of the tube to thereby compress theend portion of the tube.

In accordance with another aspect of the present invention, a tube andfitting assembly is provided which includes a fitting with an socket, ahollow pin extending concentrically in the socket, and a tube having anend portion disposed over the pin within the socket, the end portion ofthe tube being clamped between the inner surface of the socket wall andthe outer surface of the pin to form a fluid-tight connection betweenthe fitting and tube.

These, as well as other objects and advantages of the invention, willbecome apparent from the following detailed description and accompanyingdrawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an elevational view of an infusion catheter made in accordancewith the present invention;

FIG. 2 is a longitudinal cross-sectional view of the fitting and tube ofFIG. 1 but before they are permanently secured together;

FIG. 3 is an end view of the fitting of FIG. 2 without the tube;

FIG. 4 is a cross-sectional view illustrating apparatus used in themethod of permanently connecting the fitting and tube of FIG. 2together; and

FIG. 5 is a cross-sectional view of a portion of the apparatus of FIG. 4illustrating another step in the method of permanently connecting thefitting and tube of FIG. 1 together.

FIG. 6 is a view illustrating an alternative embodiment for connectingthe fitting and tube of FIG. 2 together.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT AND METHOD OF MAKINGTHE SAME

Referring now to the drawings, there is shown in FIG. 1 an infusion orintravenous catheter 10 including a fitting and tube assembly 12 made inaccordance with the present invention, connected to a needle assembly 13which includes an intravenous hollow metal needle or cannula 14 having aneedle hub 16 that is shown having a pair of oppositely extending, flatwings 17 and 18 integrally connected to the hub 16. The hub surroundsand is fixed to the needle 14. The hub and wings may be made of asuitable plastic such as polyvinyl chloride. The assembly 12 includes afitting or connector 22 fixed to one end portion of a tube 24. The otherend of tube 24 is connected to the proximal end of the needle hub 16 influid communication with needle 14. In use, the needle 14 is insertedinto the vein of a patient and the wings 17 and 18 are secured such asby taping them to the skin of a patient to maintain the needle cannulain the desired position. A source of infusion liquid can be connected tothe fitting 22 so that infusion liquid flows through tube 24 and needle14 to the vein of a patient. While the fitting and tube assembly 12 isshown connected to form an intravenous catheter 10, the assembly 12 maybe connected to form other apparatus such as associated with other typesof catheters for purposes other than the infusion of liquid into thevein of a patient.

The fitting 22 is shown in its original condition in FIG. 2, that is, inits molded condition before being permanently attached to the tube 24.As seen in FIG. 2, the fitting 22 has a conventional luer tapered bore26 and a pair of diametrically opposed luer lock ears or thread members28 and 30 at the left or proximal end of the fitting. The tapered bore26 and ears 28 and 30 are adapted to be connected with a conventionalmale luer lock connector of another device such as a luer lock connectorof a tube connected to an infusion liquid source. As also seen in FIG.3, fitting 22 has an annular recess or socket 32 having an annularsocket wall or collar 34 at the opposite or distal end of the fitting. Aconcentric, hollow pin 36 extends axially and centrally of the socket 32and is shown extending externally of the distal end of the socket wall34. Pin 36 has a bore 38 which connects with the luer tapered bore 26.The proximal end portion of tube 24 is inserted into socket 32 over pin36. Preferably, the outer diameter of the pin 36 and the inner diameterof tube 24 are formed such that the tube forms a snug or tight frictionfit with the outer surface of the pin. Generally, this step of insertingthe tube 24 into the socket 32 of the fitting 22 is performed before theother or distal end of tube 24 is connected to the needle assembly 13 orany other device.

Fitting 22 is a unitary member, preferably molded of a thermoplasticmaterial, preferably a polypropylene plastic, although other plasticssuch as polyethylene, polyvinyl chloride or others may be used in somecases. Plastic tube 24 may be made out of a suitable plastic, forexample, it may be extruded from polyvinyl chloride, although it may bemade of rubber or from other plastics such as polyethylene or urethane.As used herein, the term "plastic tube" is intended to mean a tube madeof a material such as synthetic rubber, plastic or elastomeric material.

After the tube 24 has been inserted into the socket 32 of the fitting 22as shown in FIG. 2, the fitting is inserted onto a luer tapered pin 40of a spin-forming mechanism 42 shown for illustration in FIG. 4, andwhich is employed in the process of permanently fixing the fitting 22 influid-tight, fixed connection with the tube 24. The mechanism pin 40 isconnected to a plate 44 which is schematically illustrated as beingdriven up and down on guide rails 49 by an air cylinder 46 automaticallyoperated by a cylinder control system 48. Since the tube 24 is in snug,frictional fitting relation with the pin 36 of the fitting, the tworemain together and can be handled manually or by mechanical apparatusbefore being permanently fixed together without the two separating.

The fitting and tube are shown in FIG. 4 extending into a spin-formingdie indicated generally at 50 which is mounted in fixed relation in theupper end of a driven shaft 54 mounted for rotation in bearings 56 and58 in a stationary housing 60. Shaft 54 is connected to a pulley 62which is driven by a pulley belt 64 that is, in turn, driven by a pulley66. Pulley 66 is illustrated as being driven by a motor-drive system 68through a shaft 70. The pulleys 62 and 66 may be mounted for rotation bypulley bearings 72 and 74, respectively, that are mounted on stationaryshafts 76 and 78, respectively.

The spin-forming die 50 has a die-forming cavity 79 with a formingsurface 80 which smoothly tapers radially inwardly and downwardly to anarrow end at the bottom of the die so that the surface is generallyfrusto-conical in shape. The die cavity 79 is open at the top and bottomso that the tube 24 can pass through the die during spin-formingoperations. Die 50 is of a metal such as a stainless steel and with thesurface 80 polished.

By moving the fitting 22 with the tube 24 connected to the pin 36 of thefitting into the die 50 (FIG. 4) with a downward force, such as underthe force applied by cylinder 46 to pin 40, the socket walls or collar34 of the fitting engage the rotating walls or surface 80 of die cavity79 and move toward the narrow end of the cavity. With the downward forceapplied to the pin 40 and fitting 22, the collar 34 of the fitting 22moves further into the narrowing lower portion of the die cavity 79 withthe walls of collar 34 narrowing or becoming reduced in diameter. Asfitting 22 moves further into the die 50, the collar 34 becomes slightlyextruded longitudinally or distally and is tightly clamped against theouter surface of the end of tube 24 as shown in FIG. 5. The heatgenerated by the frictional engagement between the collar 34 and therotating cavity 79 heats the collar and contributes to the process offorming the collar about the tube 24. The fitting 22 is now movedupwardly and out of the die 50 such as by pin 40 and the action of aircylinder 46. The fitting 22 and the attached tube 24 are removed frompin 40 and entirely removed from the die mechanism 42 with the fittingand tube assembly in its permanently shaped condition shown in FIG. 5.The end portion of tube 24 is tightly clamped between the inner surfaceof collar 34 and the outer surface of pin 36, as seen in FIG. 5, so thata fluid-tight, mechanically strong connection is made between thefitting 22 and tube 24.

The distal end of the tube 24 may then be connected to the proximal endof the needle hub 16 where the fitting and tube assembly is to be usedin the infusion catheter of FIG. 1.

In this way, the fitting and tube assembly 12 can be used in relativelyhigh fluid pressure systems without resulting in a leak at theconnection between the fitting and tube or separation of that.Successful fitting and tube assemblies were made which employed afitting molded of a polypropylene plastic in the shape of fitting 22.The inside diameter of the collar 34 was about 3.76 millimeters (mm);the outside diameter at the distal end of the socket was about 4.52 mm;the outside diameter of pin 36 was about 1.778 mm; and the diameter ofthe pin bore 38 was about 0.965 mm. The pin 36 had an axial lengthmeasured from the bottom of the socket of about 5.84 mm and extendedoutwardly about 1.52 mm from the free end of the socket wall 34. Theradial dimension between the inner surface of wall 34 and the outersurface of pin 36 was about 0.991 mm. The plastic tube was extruded frompolyvinyl chloride and had inner and outer diameters of about 1.34 mmand 2.18 mm, respectively, so that the radial thickness of the tube sidewall was about 0.42 mmm. The finished fitting and tube assembly wastested under a pressure of 45 psi without leakage.

The spin-forming die used to make those assemblies was similar in shapeto die 50. The die was rotated at a speed of 2550 rpm, a force of about24 lbs. was applied to the fitting during insertion into the die, andthe time of forming was about 1 second. While specific materials for thetube and fitting, specific die speed, applied force, and forming timehave been mentioned herein for purposes of illustration, it will beapparent to those skilled in the art that variations in the above can bemade and good fitting and tube assemblies obtained. For example, the diespeed, in some cases, may be a speed between 1000 and 3000 rpm. Also, insome cases, the force applied on the fitting during forming may be, forexample, between 20 and 30 lbs. Also, this method of making tube andfitting assemblies is especially important where the tubes are ofrelatively small size, for example, tubes having outer diameters belowabout 6.25 mm.

No solvent or adhesive is required to secure the fitting and tubetogether in the present spin-forming method. This, of course, avoids thedisadvantages of applying such a solvent or adhesive, storing it, andthe undesirable gases and smells that result from the use of solvents oradhesives. Tube and fitting assemblies spin-formed as discussed aboveprovide a strong assembly that can withstand relatively high forcestending to pull the fitting and tube apart.

FIG. 6 illustrates a method of making a tube and fitting assembly inwhich the fitting and tube are rotated while the die is not rotated. Asseen in FIG. 6, a pulley 100, driven by a pulley belt 102, rotates a pin104 carrying a fitting 106 similar to fitting 22 in shape. A tube 108having one end portion disposed on the hollow pin (not shown) of thefitting extends into an end collar 110 of the fitting. A forming die 112is illustrated as being movable up and down as indicated by the arrowsadjacent the die. In this case, the die moves upwardly onto the rotatingcollar 110 of the fitting causing the collar to be spin-formed about theupper end of tube 108 to provide a finished assembly with the tubeclamped between the formed collar 110 and pin 104. The finished assemblyin this case is similar to that shown in FIG. 5 in connection withassembly 12.

It will now be apparent that the various objects and advantages of thepresent invention have been met. As various changes may be made in theabove construction and method of making the construction withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdrawing shall be interpreted as illustrative and not in a limitingsense.

I claim:
 1. A method of making a tube and fitting assembly comprisingthe steps of providing a formable fitting having an end socket and a pinhaving a bore therethrough extending concentrically within the socket,inserting one end portion of a plastic tube onto the pin and into thesocket, providing a die having a die-forming cavity narrowing toward oneend thereof, effecting relative rotation of the fitting and die andrelative axial movement of the fitting and die toward each other withthe walls of the socket engaging the walls of the die-forming cavity andwith the fitting moving in a direction toward the narrow end thereof toinwardly form the walls of the socket against the outer surface of thetube, and separating the fitting with the tube attached thereto from thedie.
 2. The method of claim 1 wherein the die is rotated to effect saidrelative rotation.
 3. The method of claim 2 wherein the speed ofrotation of said die is between about 1000 and 3000 revolutions perminute.
 4. The method of claim 1 wherein said fitting is formed of amaterial including polypropylene.
 5. The method of claim 4 wherein thedie is rotated and at a speed of about 2550 revolutions per minute. 6.The method of claim 5 wherein a force is applied to said fitting duringsaid axial movement of between about 20 and 30 lbs.
 7. The method ofclaim 6 wherein a force of about 24 lbs. is applied to said fittingeffecting said relative axial movement.
 8. The method of claim 1 whereinthe socket walls are maintained in engagement with the walls of thedie-forming cavity for about one second.
 9. The method of claim 1wherein the fitting is rotated to effect said relative rotation.
 10. Themethod of claim 1 wherein said fitting has a luer taper bore open at theopposite end of the fitting connected in fluid communication with thebore of the pin.
 11. The method of claim 10 wherein the fitting has luerlock ears at the opposite end thereof.
 12. The method of claim 1 whereinthe die socket is genrally frusto-conical in shape.
 13. A method ofmaking a tube and fitting assembly comprising the steps of providing athermoplastic fitting having an end socket and a pin having a boretherethrough extending concentrically within the socket, inserting oneend portion of a pastic tube onto the pin in tight frictional connectiontherewith and into the socket, providing a die having a die-formingcavity narrowing toward one end thereof, rotating the die at apredetermined speed, inserting the socket with the tube end portion onthe pin into the cavity and urging the fitting under a predeterminedforce in a direction toward the narrow end of the cavity so that theouter surface of the walls of the socket engage the walls of the cavitywhile the die is rotating to spin-form the walls of the socket againstthe outer surface of the tube for a predetermined length of time tothereby compress the tube between the inner surface of the spin-formedwalls of the socket and the outer surface of the pin, and removing thefitting with the tube attached thereto from the die.
 14. The method ofclaim 13 wherein said predetermined speed is between about 1000 and 3000revolutions per minute, and said predetermined force is between about 20and 30 lbs.
 15. The method of claim 14 wherein said predetermined lengthof time is between about 1/2 and 2 seconds.
 16. The method of claim 15wherein said fitting is of polypropylene.
 17. The method of claim 13wherein said predetermined speed is about 2550 revolutions per second,said predetermined force is about 24 lbs., and said predetermined lengthof time is about 1 second.
 18. The method of claim 1 wherein the outerdiameter of the tube is less than about 6.25 mm.
 19. The method of claim1 wherein the formed walls of the socket clamp the tube against the pin.20. The method of claim 19 wherein the tube is in snug fitting relationon the pin before the walls of the socket clamp the tube against thepin.